1. Field of the Invention
The present invention relates to a resist pattern, to a process for the formation thereof, and to a process for the formation of a wiring pattern. More particularly, it relates to a technique for the formation of a resist pattern which is stable in shape, dimensions, accuracy and other characteristics. Furthermore, it relates to a process for the formation of a fine wiring pattern by plating or by a lift off process. The resist pattern, the process for the formation of the resist pattern, and the process for the formation of a wiring pattern can be suitably employed for a semiconductor device manufacturing process or electronic parts manufacturing process which require fine patterning.
2. Description of the Related Art
As processes for the formation of a thick fine wiring having a thickness exceeding 1 xcexcm, there may be mentioned a semi-additive (plating) process as shown in FIGS. 9A to 9G, and a lift off process as illustrated in FIGS. 10A to 10F.
Initially, the semi-additive process will now be described. According to this process, a feed film 32 (or plating base) of a metallic material is formed on a substrate 31 (FIG. 9A), and then a positive resist 33 is applied onto the feed film 32 (FIG. 9B). Subsequently, the resist 33 is exposed to ultraviolet radiation through an aperture 34a of a photomask 34 (FIG. 9C), and then is subjected to development (FIG. 9D). A region of the resist 33 exposed to ultraviolet radiation becomes soluble, and the exposed region is hence dissolved by development to give a resist pattern 35 rectangular in cross section.
After this step, a voltage is applied to the feed film 32 to conduct electroplating, and a plating metal is precipitated on the feed film 32 in a region not covered by the resist pattern 35 (FIG. 9E), to form a plated film 36. After the completion of plating, the resist pattern 35 is stripped (FIG. 9 F), and the feed film 32 is removed by etching in a region not covered by the plated film 36 to give a target wiring pattern 37 on the substrate 31 (FIG. 9G).
Next, the lift off process will be described. According to this process, a negative resist 42 is applied (FIG. 10B) onto the surface of such a substrate 41 as shown in FIG. 10A, and the resist 42 is then exposed to ultraviolet radiation through an aperture 43a of a photomask 43 (FIG. 10C), and the exposed resist is subjected to development (FIG. 10D). The resist 42 in a region exposed to ultraviolet radiation becomes insoluble, and the exposed region remains even after the development to give a resist pattern 44 which is of a reversed taper shape in cross section.
Next, an electrode material 45 is deposited all over the substrate 41 from above the resist pattern 44 (FIG. 10E), and the resist pattern 44 and the electrode material 45 deposited on the resist pattern 44 are stripped off to give a target wiring pattern 46 on the substrate 41 (FIG. 10F).
As is apparent from the aforementioned explanation, both the semi-additive process and lift off process require forming a resist pattern having a thickness greater than the thickness of a target wiring, as their operations demonstrate, and thus require forming a comparatively thick resist pattern. In addition, the resist pattern formed by the semi-additive process must be rectangular in cross section, and that formed by the lift off process must be of a reverse taper shape in cross section.
Furthermore, both of the semi-additive process and lift off process are characterized in that a film of a wiring material is formed after the formation of a resist pattern to give a wiring pattern. The dimensions, shape and accuracy of the wiring pattern therefore reflect the dimensions, shape and accuracy of the resist pattern. Consequently, it is important to retain the shape of the resist pattern until the formation of a film of the wiring material is completed in order to provide a fine wiring pattern sufficiently having target dimensions, shape and accuracy.
According to conventional processes for the formation of a resist pattern, however, the following results, for example, occur when the thickness of a resist film to be formed is increased:
(1) volumetric shrinkage of the resist pattern due to degassing (gas emission) when the resist is baked in a photolithography step,
(2) defective film of the wiring material because of a collision between flying particles of the wiring material and gas particles, which gas particles are derived from degassing with increasing temperature in the formation of a film of the wiring material, and
(3) stress of the wiring material. The resist sags or deforms because of these results, and an ideal shape of the resist cannot be maintained, and in consequence, a target fine wiring pattern cannot be obtained when a film of the wiring material is formed.
The present invention has been accomplished to solve the aforementioned technical problems, and its object is to provide a process for the formation of a wiring pattern, which can yield a fine wiring pattern having target dimensions, shape and accuracy while suppressing the deformation of a resist pattern due to heat or stress.
The resist pattern according to the present invention includes a plurality of depressions formed on its surface, the depressions not reaching the back of the resist pattern.
As the present resist pattern has a plurality of depressions formed on its surface, which depressions neither penetrate the pattern nor reach the back of the resist pattern, the volume of the resist pattern can be smaller and the surface area thereof can be greater than normal. Since the volume of the resist pattern can be decreased by forming depressions on the resist pattern as thus described, the volume of degassing upon baking of the resist pattern can be reduced, and the volumetric shrinkage of the resist pattern can therefore be decreased. Furthermore, by making the resist pattern pectinate or comb-like in cross section, a stress applied from the wiring pattern can be decreased and hence deformation due to the stress in the resist pattern can be mitigated.
In addition, as the surface area of the resist pattern is increased, gas can sufficiently be emitted from the resist pattern when the resist pattern is baked. The volume of emitted gas in the film formation step can therefore be reduced to avoid scattering of flying particles of the wiring material by gas particles emitted from the resist pattern and to ensure attachment of a film on the substrate. Consequently, the deformation of the resist pattern due to, for instance, volumetric shrinkage of the resist pattern can be suppressed, and the formation step of a film of the wiring material is not hindered by gas emission from the resist pattern, resulting in the formation of a precise and satisfactory wiring pattern. In this connection, as the depressions do not reach the back of the resist pattern, they do not affect the pattern shape of the wiring pattern.
In particular, a thick resist having a thickness of 2 xcexcm or more often suffers volumetric shrinkage and/or deformation, and the application of the configuration to a resist having a thickness of 2 xcexcm or more yields marked advantages.
A process for the formation of a resist pattern according to the present invention includes the steps of: exposing a resist through a photomask and developing the exposed resist, the photomask having a pattern whose line width is equal to or less than a resolution limit, to form depressions on the surface of a resist pattern, the depressions not reaching the back of the resist pattern.
According to the present process for the formation of a resist pattern, depressions can be formed on the surface of a resist pattern in a conventional manner, which depressions do not reach the back of the resist pattern, only by the use of a photomask having a pattern whose line width is equal to or less than the resolution limit. Consequently, conventional exposure equipment or the like can be used as intact, and resist patterns can be formed with facility at low costs.
A process for the formation of metalization according to the present invention includes the steps of: applying a resist onto an underplate feed film, exposing the resist through a photomask, the photomask having a pattern whose line width is equal to or less than a resolution limit, developing the exposed resist to form groove depressions on the surface of a resist pattern, the depressions not reaching the back of the resist pattern, precipitating a plating metal on the feed film in a region not covered by the resist pattern, stripping the resist pattern after the precipitation, and selectively removing the feed film in a region not covered by the plating metal.
The aforementioned process is a process for the formation of a wiring pattern according to a so-called semi-additive process. The application of the process explained above to this process can reduce the volume of, and can increase the surface area of, the resist pattern, and therefore can decrease the volumetric shrinkage of the resist pattern upon baking to give a target shape of the resist pattern. Consequently, a target fine wiring pattern can be formed.
A process for the formation of a wiring according to another aspect of the present invention includes the steps of: applying a resist onto a substrate, exposing the resist through a photomask, the photomask having a pattern whose line width is equal to or less than a resolution limit, developing the exposed resist to form groove depressions on the surface of a resist pattern, the depressions not reaching the back of the resist pattern, depositing a metallic material on the resist pattern and on the substrate, and subsequently stripping the resist from the substrate to remove the metallic material on the resist.
The process just mentioned above is a process for the formation of a wiring pattern according to a so-called lift off process. When the process explained above is applied to this process, the volume of the resist pattern can be smaller and its surface area can be larger than normal, and therefore the volume of degassing with an increasing temperature in the deposition of a metallic material can be decreased, and the volumetric shrinkage and/or deformation of the resist pattern can significantly be suppressed. In addition, by forming projections and depressions on the surface of the resist pattern, the stress of the metallic material can be dispersed in direction, and a stress applied on the edges of the resist pattern can markedly be decreased. By these effects, the deformation of the resist pattern caused by the film formation of the metallic material can be prevented. Moreover, the shape of the resist pattern can be maintained even after the film formation, and a target wiring pattern can be formed by lift-off, and a resist pattern having an exactly intended shape, dimensions, accuracy and the like can be obtained.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.